I have recently found an old 10 gallon aquarium in my garage with practically all the caulk chewed off by something lol and I was going to clean it and put my betta fish in there and give him a full setup, but I was most likely going to scrape off all the little bits of caulk and redo it, I had a few questions

is it even caulk or is it a special glue? Im talking about the clear stuff along the corners of the tank that holds the glass together

It is Aquarium Sealer...you can't just use silicon sealer from Home depot.. It is very inexpensive.. you get it at the LFS..You would be better off just getting a new 10 Gallon..they are probebly cheaper and less hassle than trying to clean and seal the old one.

I would not use an old aquarium that's been sitting in a garage ..when a new 10 gallon is so cheap..there could be mold & fungus spores in there and when you add water......it could be a problem..you can do what you like , I'm just saying I would toss it and get new if my pet's health was at stake